I agree, some colonies are the size of whats considered to be frags. When I think of a frag it will fit on a basic 3/4 - 1 inch plug and when I think of mature colony, about the size of my hand opened.
i prefer frags, they take a while to grow into maturity, but when they do they adapt to the flow and take off, ive found colonys have already started one growth pattern and when placed in an area that makes them change, it disrupts growth quite a bit
My 2 cents - with the explosion of smaller tanks, and cheaper lighting technology more people are trying reefs that didn't before (myself included). Keeping that trend in mind, these smaller tanks and tighter budget group are looking for frags and not colonies. Variety is the name of the game and the best/only way to get that done is with frags in a small tank. So I say focus on frags, and have some high end colonies on hand for your clients with fat wallets.
Colonies. I can usually make back what I payed for a colony by fraging it and selling the frags to people in my club, and I'm left with a good chunk to watch grow.